Molecules having various molecular weights can be separated across a semi-permeable membrane. The membrane by virtue of its composition, and consequently its porosity, allows relatively smaller molecules, that is, equal to or less than a particular molecular weight cutoff, to pass through the membrane. Relatively larger molecules are unable to pass through the membrane. Such membrane systems are often used in laboratory research and commonly referred to as dialysis membranes. Common applications of dialysis membranes are: exchanging one sample buffer for another buffer, sample desalting, molecular separations, and sample concentration.
Some methods use a dialysis membrane as the sole molecular exchange between a sample and dialysate. A widely used research method ties or clamps one end of the dialysis membrane, in the shape of a tube, to form a sack. The sample is added to the interior of the dialysis membrane sack which is then tied or clamped at the non-tied end. The sack, now a closed vessel, is submerged into the dialysate. To improve the dialysis process in terms of handling, reliability and speed, a variety of devices have been designed to house the dialysis membrane.